This invention refers to a method of reducing the lead and/or barium emission of articles of crystal glass containing lead and/or barium, particularly so-called lead crystal and baryte glasses, on contact with a liquid phase, particularly aqueous, aqueous-acidic, alcoholic and aqueous-alcoholic liquids such as acetic acid solutions, wine, whiskey, liqueurs and the like.
It is common knowledge to process crystalline glasses containing lead and up to 32% lead crystal glasses, as well as baryte glasses with up to 7% by weight of BaO, uncut, cut or pressed, to form drinking glasses, bowls, vases, etc. The surface is greatly enlarged by the often extensive cutting, and the many edges produce optimal reflection of the impinging light and hence the desired brilliance of the surface.
For some four to five years, following great improvement in analytic technology, drinking glasses and bottles containing lead and barium have been tested for possible lead and/or barium emission in an acidic medium and, for bottles, in an alcoholic medium.
Tests have shown that the emissions are greatest in the first 24 hours and that they then asymptotically approach a saturation value.
The lead emission in an acidic medium is measured with a 4% acetic acid solution at 20.degree. C. as a function of time.
Furthermore, subjecting crystal glasses of the kinds described above to acid polishing is generally known. For instance, this can be done with a mixture of a 20 to 40% hydrofluoric acid and a 15 to 30% sulfuric acid. In addition, in EP-A 0 106 301 a method is known for polishing glass objects in a polish bath containing sulfuric acid and hydrofluoric acid, wherein acids having a dissociation constant greater than that of the hydrofluoric acid are added to control the fluorine ion concentration. With this method a polish with a greatly reduced surface wear-off can be achieved.
A disadvantage of the known crystal glasses is their lead and/or barium emission on contact with liquid phases.